A vehicle distance control device is known in the art as one of control devices for a vehicle automatic running, other than a control device for a vehicle constant speed running (which is generally called as a cruise control system). The control device for the vehicle constant speed running is such a system, in which a vehicle speed is controlled at a preset vehicle speed so that the vehicle runs at such a preset constant vehicle speed. In the system of this kind, an opening degree of a throttle valve is automatically controlled without an operation of an acceleration pedal by a vehicle driver, such that an actual vehicle speed detected by a vehicle speed sensor may coincide with the preset vehicle speed.
In the vehicle distance control device, for example, as disclosed in Japanese Patent Publication No. H6-229279, an electronic throttle control system is controlled. In the electronic throttle control system, a vehicle distance toward a front vehicle as well as a vehicle speed of the front vehicle is detected by a sensor (e.g. a camera) mounted on a vehicle, and a demand vehicle acceleration (a target acceleration) for the vehicle is calculated based on the information, such as the vehicle distance, a speed difference between its own vehicle and the front vehicle, and the vehicle speed of its own vehicle. Then, a target opening value of a throttle valve is calculated based on the above-calculated demand vehicle acceleration, a position of a transmission gear (a position of a shift lever), and the vehicle speed of its own vehicle.
A number of vehicles, in which the control device for the vehicle constant speed running is mounted as a standard equipment, is increasing, because the control device for the vehicle constant speed running can be manufactured at a low cost and formed as a simple structure, for example, a structure having a speed setting switch. In addition, since a control logic for the control device for the vehicle constant speed running is not complicated, a function for the vehicle constant speed running control is often incorporated into an electronic control unit (ECU) for controlling the electronic throttle control system.
On the other hand, there are not many vehicles in which the vehicle distance control device is mounted, because such device is still expensive as a result that the control device needs the camera for detecting the vehicle distance to the front vehicle and the vehicle speed of the front vehicle, and so on. Accordingly, the vehicle distance control device is mounted in the vehicle as an optional equipment, or mounted in high-grade vehicles as the standard equipment. In addition, since a control logic for the vehicle distance control device is more complicated than that of the vehicle constant speed running control, a function for the vehicle distance control is generally formed as an external module, separately from the ECU for the electronic throttle control system.
In such a case, it is necessary to newly develop a system, so that the ECU of the electronic throttle control system may read-in a control signal from the external module, and converts the control signal into the target opening value of the throttle valve.
There are other external modules for the vehicle, other than the external module for the vehicle distance control, such as TRC (a traction control system), ABS (an anti-block braking system), and so on. In the case that those external modules are mounted in the vehicle, the same problem must be solved, namely the ECU for the electronic throttle control system should be modified to read-in control signals from those external modules and to convert the control signals into the target opening value of the throttle valve.